Liquid driven downhole drilling machine

ABSTRACT

In a liquid downhole drilling machine, the guiding bushing ( 31 ) for the drill bit is rotatably journaled in the housing ( 11, 12 ) and, via a one-way coupling ( 29 ), coupled to a turning sleeve ( 22 ) that has axial ridges ( 24 ) that bound a number of chambers ( 25, 26, 27 ) and form turning pistons for turning the turnable sleeve to and fro. A number of these chambers are coupled to be pressurized and depressurized simultaneously with said pressure chamber ( 47 ) with the piston area ( 46 ) for urging the piston hammer ( 30 ) forwards. As a result, the drill bit ( 13 ) will be indexed a defined angle between each impact so that the button inserts of the drill bit will change contact points with the rock between every impact and fragment the rock efficiently. The drill tube is not rotated.

TECHNICAL AREA OF THE INVENTION

This invention relates to a liquid driven downhole drilling machinecomprising a housing, a drill bit mounted in a guiding bushing to beangularly fixed but axially limitedly movable thereto, a piston hammerarranged to impact on a shank of the drill bit, and a valve forcontrolling reciprocation of the hammer piston, the valve alternatelypressurising and depressurising a pressure chamber in which there is apiston area that urges the hammer piston forwards when the chamber ispressurised.

BACKGROUND OF THE INVENTION

Liquid driven downhole drilling machines of this kind are often usedwith drill tubes that are added to one another and the thus formed drillstring is rotated so that the drilling machine and thereby the drill bitis indexed between each impact of the piston hammer. The drill bit isangularly fixed in the housing. When deep holes are drilled, althoughthe rotation of the upper end of the drill tube is continuous, thefriction between the drill tube and the borehole wall will sometimesmake the rotation of the lower end of the drill tube uneven. The drilltube will act as a torsion spring and instead of being indexed evenlybetween the impacts of the piston hammer, the drilling machine will notbe turned while there are several impacts and then it will be rapidlyturned. This slip-stick effect reduces the drilling rate and increasesthe drill bit wear.

In liquid driven downhole drilling machines, the power liquid issupplied through the drill tube and the return stroke of the pistonhammer is retarded hydraulically which induces pressure spikes since thepiston hammer will then force liquid out into the drill tube. This willresult in high stresses and also in a reduction of power efficiency.Attempts have been made to have an accumulator in direct connection tothe drilling machine but hitherto there is no good solution to thisproblem.

OBJECT OF INVENTION

It is an object of the invention to improve the indexing between theimpacts of liquid driven downhole drilling machines in use. Anotherobject is to reduce the pressure spikes at the inlet of the power fluidto the machine and at the same time improve the power efficiency.

These objects are achieved by having the guiding bushing rotatablyguided in the housing and, via a one-way coupling, coupled to a turnablesleeve that has axial ridges that bound a number of pressure chambersand forms turning pistons for turning the turnable sleeve to and fro, anumber of these chambers being coupled to be pressurised anddepressurised simultaneously with said pressure chamber with the pistonarea for urging the piston hammer forwards.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a longitudinal section through the front portion of adownhole drilling machine in accordance with the invention.

FIG. 1 b Is a longitudinal section through the rear portion of the samedownhole drilling machine.

FIG. 2 is a section taken along line 2—2 in FIG. 1 a.

FIGS. 3 and 4 are the same transverse section as FIG. 2, but they howsome elements in other mutual positions.

FIG. 5 is a transverse section taken along line 5—5 in FIG. 1 a.

DESCRIPTION OF AN ILLUSTRATED AND PREFERRED EXAMPLE OF THE INVENTION

The liquid driven downhole drilling machine shown on the figures has amachine housing that comprises a machine tube 11 the upper portion ofwhich has a non-illustrated back head arranged to be coupled to a drilltube that supplies drive fluid, usually water or a suspension ofbentonite in water. The middle portion of the downhole drilling machineis not shown. An outer tube 12 is fixedly mounted, screwed, to the frontportion of the machine tube and a drill bit 13 extends with its shank 14into the outer tube. An end sleeve 15 is screwed to outer tube 12 andclamps a follower sleeve 16 against an axial bearing 17 that takessupport against an inner shoulder 18 in the outer tube 12. The followersleeve is rotatably journaled in the outer tube 12. The forward end ofthe machine tube 11 has a reduced diameter and it has a plurality ofridges 20, FIG. 2. A turning sleeve 22 is journaled between the frontend of the machine tube 11 and the outer tube 12. It has inward-directedridges 24. A plurality of sealed chambers 25,26,27 are defined betweenthe ridges 20 and 24. The axial portion of the machine tube radiallyinside of the ridges 20 forms a short forward guide for a piston hammer30.

A one-way coupling 28 of a conventional type having toggle elements 29is coupled between the follower sleeve 16 and the turning sleeve 22.

The shank 14 of the drill bit 13 has a splined connection with a guidingbushing 31 that is screwed to the follower sleeve 16 and clamps a stopring 32 axially against shoulder on the follower sleeve. The stop ring32 is axially split so as to mountable and it extends into a recess 33in the shank of the drill bit so that it prevents the drill bit fromfalling out but allows a limited axial movement of the drill bit. Thedrill bit has an non-illustrated central channel for conveying flushingwater to grooves in the front end of the drill bit.

In the front end of the machine tube 11, there is a valve 40 in a valvehousing 41 and the valve housing has a tube 42 that extends into thelongitudinal channel 43 of the piston hammer 30. The non-illustratedback head of the machine clamps the valve housing against a distancesleeve 44 that takes support with its forward end against a shoulder inthe machine tube 11. The distance sleeve 44 seals against the machinetube 11 and it has longitudinal grooves that form a number of channels25 a between the distance sleeve and the machine tube. The piston hammer30 has a head 45 that is guided both exteriorly in the distance sleeve44 and interiorly on the tube 42. The piston is thus guided only byshort guiding areas at its ends and a major part of the length of thepiston is unguided since there is an annular space 49 between the pistonand the distance sleeve 44. Behind the head 45 of the piston hammer isformed an annular piston surface 46 in an annular cylinder chamber 47(pressure chamber) and the head forms a smaller annular piston surface48 in the cylinder chamber 49 (pressure chamber) that is formed in thespace that extends all the way between the two guiding areas of thepiston hammer. The cylinder chamber 49 is constantly coupled to the highpressure liquid through channels that are parallel with the channels 25a so as to provide constantly a rearward-directed force on the on thepiston whereas the valve 40 alternately connects the cylinder chamber 47to the high pressure liquid and to the tube 42 that is connected to theflushing grooves in the drill bit via the through channel 43 of thepiston. The tube 42 has thus always low pressure and the out-flowingliquid is used to flush the debris out of the borehole. Since the pistonarea 46 is much greater than the piston area 48, the piston hammer willreciprocate and impact on the shank of the drill bit with a frequencythat can be for example 100 Hz.

The channels 25 a lead from the cylinder chamber 47 to the six chambers25 in FIG. 2 so that these chambers 25 will be alternately pressurisedand depressurised. Ports 26 a lead from the constantly pressurisedcylinder chamber 49 to the two chambers 26 in FIG. 2 so that thesechambers 26 will be constantly pressurised and ports 27 a connects thefour chambers 27 to the chamber 50 that is formed at the end surface ofthe drill bit shank. The four chambers 27 are therefore constantlydepressurised.

FIG. 3 shows the position of turning of the turning sleeve 22 when thechambers 25 have low pressure. The two chambers 26 are the only chambersthat are pressurised and the sleeve 22 has therefore turnedcounterclockwise into its end position in which its ridges 24 takesupport against the ridges 20 of the machine tube 11.

FIG. 4 shows the position of turning of the turning sleeve 22 when notonly the two chambers 26 but also the four chambers 25 are pressurised.The two chambers 26 tend to turn counter-clockwise but the six chambers25 tend to turn clockwise, and the force from the four chambers hastherefore turned the turning sleeve 22 clockwise into the end positionin which its ridges take support against the ridges of the machine tube.

The turning sleeve 22 will thus be turned to and fro trigged by thepressure at the rear piston surface of the piston hammer, that is, it istrigged by the impact cycle of the hammer. Since the reverse preventiondevice 29, the one-way clutch, couples the turning sleeve 22 with thefollower sleeve 16, the latter will rotate clockwise relative to themachine tube 11. The follower sleeve will follow the turning clockwiseof the turning sleeve but stand still during the turningcounter-clockwise of the turning sleeve. As a result, the drill bit 31will turn a defined angle (be indexed) between each impact so that thebutton inserts of the drill bit will change their points of contact withthe rock between every impact and they will fragment the rockefficiently. The drill tube need therefore not be rotated and instead ofextension tubes, a coil tubing can be used, that is, a bendable drilltube without joints, which can be uncoiled from a coil.

When the piston hammer is in its rearward stroke and the valve 40switches to its position for pressurising the rear cylinder chamber 47,the piston hammer will be retarded by this pressure and turn into itsforward stroke. During the retardation of the piston, the cylinderchamber 47 will reduce in volume and the drive liquid will be forced outof the chamber, which will result in a pressure increase and power lossbecause of the flow. The six chambers 25 of the turning device arecoupled to the cylinder chamber 47 and they can therefore take up theliquid forced out of cylinder chamber, which reduces the losses and atthe same time makes the turning efficient. The need for an accumulatorat the inlet of the impact motor is reduced as well.

In the chosen pattern of pressure chambers 25,28,27 and turning pistons24 with twelve pressure chambers, there will be symmetry with respect tothe turning forces and the radial forces, which reduces the bearingforces in the sleeve 5. Another pattern can be chosen and still theturning pressure chambers can be coupled to the pressure chamber fordriving the piston hammer forwards. The invention can be applied topiston hammers that are driven by another principle than the one thatapplies alternating pressure for the work stroke of the piston andconstant pressure for the return stroke.

1. Liquid driven downhole drilling machine comprising a housing (11,12), a drill bit (13) mounted in a guiding bushing (31) to be angularlyfixed but axially limitedly movable thereto, a piston hammer (30)arranged to impact a shank (14) of the drill bit, and a valve (40) forcontrolling reciprocation of the piston hammer, the valve alternatelypressurising and depressurising a pressure chamber (47) in which thereis a piston area (46) that drives the piston hammer forwards when thechamber is pressurised, wherein the guiding bushing (31) is rotatablyguided in the housing (11, 12) and, via a one-way coupling (29), coupledto a turnable sleeve (22) that has axial ridges (24) that bound a numberof chambers (25, 26, 27) and form turning pistons for turning theturnable sleeve in a first and second direction, a number of thesechambers being coupled in parallel with said pressure chamber (47) so asto be pressurised and depressurised simultaneously therewith.